This invention relates to an aluminosilicate zeolite designated UZM-8 a method of preparing the zeolite and various uses thereof. These zeolites can be used as catalysts in processes such as xylene isomerization and ethylbenzene synthesis.
Zeolites are crystalline aluminosilicate compositions which are microporous and which are formed from corner sharing AlO2 and SiO2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared are used in various industrial processes. Synthetic zeolites are prepared via hydrothermal synthesis employing suitable sources of Si, Al, as well as structure directing agents such as alkali metals, alkaline earth metals, amines, or organoammonium cations. The structure directing agents reside in the pores of the zeolite and are largely responsible for the particular structure that is ultimately formed. These species balance the framework charge associated with aluminum and can also serve as space fillers. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure. Zeolites can be used as catalysts for hydrocarbon conversions, which can take place on outside surfaces as well as on internal surfaces within the pore.
Applicants have synthesized a new family of materials designated UZM-8. The UZM-8 compositions are aluminosilicates having Si/Al molar ratio from about 6.5 to about 35. The UZM-8 compositions show unique x-ray diffraction patterns compared to other known zeolites. These UZM-8 compositions are prepared from aqueous reaction mixtures containing either organoammonium compounds or a mixture of organoammonium compounds and alkali and/or alkaline earth compounds. The organoammonium compounds used to make UZM-8 are non-cyclic nor contain cyclic substituents and are generally quite simple. Preferred examples of organoammonium compounds used to make UZM-8 include the diethyldimethylammonium (DEDMA), ethyltrimethylammonium (ETMA) or hexamethonium (HM) cations.
Although UZM-8 compositions have some similarities to a layered material identified as MCM-56, there are sufficient differences that UZM-8 compositions are structurally different from MCM-56 materials and thus are unique new zeolites structures. The preparation of MCM-56 is disclosed in U.S. Pat. No. 5,362,697 where it is stated that MCM-56 is prepared from a reaction mixture containing a combination of alkali metals and hexamethylene imine (HMI) as directing agents and requires that the silica source be a predominately solid silica source comprising at least 30 wt. % SiO2. It is further stated in the ""697 patent that the reaction must be stopped and quenched at a time before significant amounts of MCM-49 form in the reaction mixture. The synthesis of MCM-49 is disclosed in U.S. Pat. No. 5,236,575 and again involves a combination of alkali metals and HMI structure directing agents plus a predominately solid silica source comprising at least 30 wt. % SiO2. Upon calcination the MCM-49 composition is not readily distinguishable from calcined MCM-22 which has the MWW framework topology. It is further stated in J. Phys. Chem., 1996, 100, p.3788-3798, that in the as-synthesized form MCM-49 has essentially the MWW topology. Thus, MCM-56 is an intermediate structure in the formation of MCM-49 which in the calcined form is virtually the same as MCM-22 both of which have the MWW structure. The ""697 patent further describes the MCM-56 as a layered structure in both its as-synthesized and calcined forms based on the claimed swellability of the material.
In contrast to MCM-56, UZM-8 is not an intermediate in the formation of MCM-49. Additionally, the UZM-8 materials can be synthesized from an alkali free reaction mixture using an organoammonium cation such as DEDMA cation that offers great stability and robustness without the formation of MCM-49 or other impurities. However, in the HMI/Na system, varying the relative amount of amine structure directing agent to alkali metal and/or alkaline earth metal compound can yield either the MCM-56/MCM-49 system with higher relative alkali content or a precursor to MCM-22 with lower relative alkali content. Reaction conditions, mainly temperature and time, are used to distinguish MCM-56 and MCM-49 in the higher alkali content system that is difficult to control, leading to the requirement for quenching the MCM-56 reaction mixture before significant amounts of MCM-49 form. Finally, UZM-8 is a layered material in that the as-synthesized form is swellable and has a x-ray diffraction pattern that is distinguishable from MCM-56.
The UZM-8 materials of this invention are thermally stable and can be used in their acidic forms as catalysts in hydrocarbon conversion processes, including ethylbenzene synthesis and xylene isomerization, but also in separation processes, adsorption, and ion-exchange applications.
As stated, the present invention relates to a family of aluminosilicate and substituted aluminosilicate zeolites designated UZM-8. Accordingly, one embodiment of the invention is a microporous crystalline zeolite having a layered framework of at least AlO2 and SiO2 tetrahedral units and a composition on an as-synthesized and anhydrous basis expressed by an empirical formula of:
Mmn+Rrp+Al1-xExSiyOz
where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, xe2x80x9cmxe2x80x9d is the mole ratio of M to (Al+E) and varies from 0 to about 2.0, R is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium, protonated amines, protonated diamines, protonated alkanoamines and quaternized alkanolammonium, xe2x80x9crxe2x80x9d is the mole ratio of R to (Al+E) and has a value of about 0.05 to about 5.0, xe2x80x9cnxe2x80x9d is the weighted average valence of M and has a value of about 1 to about 2, xe2x80x9cpxe2x80x9d is the weighted average valence of R and has a value of about 1 to about 2, E is an element selected from the group consisting of gallium, iron, boron, chromium, indium and mixtures thereof, xe2x80x9cxxe2x80x9d is the mole fraction of E and has a value from 0 to about 1.0, xe2x80x9cyxe2x80x9d is the mole ratio of Si to (Al+E) and varies from about 6.5 to about 35 and xe2x80x9czxe2x80x9d is the mole ratio of 0 to (Al+E) and has a value determined by the equation:
z=(mxc2x7n+rxc2x7p+3+4xc2x7y)/2
and is characterized in that it has the x-ray diffraction pattern having at least the d spacings and relative intensities set forth in Table A.
Another embodiment of the invention is a process for preparing the crystalline microporous zeolite described above. The process comprises forming a reaction mixture containing reactive sources of R, Al, Si and optionally M and E and reacting the reaction mixture at reaction conditions which include a temperature of about 85xc2x0 C. to about 225xc2x0 C., for a period of time of about 1 day to about 28 days, the reaction mixture having a composition expressed in terms of mole ratios of the oxides of:
aM2/nO:bR2/pO:1-cAl2O3:cE2O3:dSiO2:eH2O
where xe2x80x9caxe2x80x9d has a value from 0 to about 25, xe2x80x9cbxe2x80x9d has a value of about 1.5 to about 80, xe2x80x9ccxe2x80x9d has a value of 0 to about 1.0, xe2x80x9cdxe2x80x9d has a value of about 10 to about 100, xe2x80x9cexe2x80x9d has a value of about 100 to about 15000.
Yet another embodiment of the invention is a hydrocarbon conversion process using the above-described zeolite. The process comprises contacting the hydrocarbon with the zeolite at conversion conditions to give a hydroconverted hydrocarbon.